1. Graph a generalization of Exhibit 4.5 that includes portfolios with short positions in one of the two investments.
2. The S&P 500 stock index portfolio had returns of 30.55 percent in 1991, 7.67 percent in 1992, 9.99 percent in 1993, 1.31 percent in 1994, and 37.43 percent in 1995. What is the estimate of the expected return and variance of the S&P 500 using only these data?